Language for track statistics tags makes no sense
currently, mkvmerge writes track statistics tags with both
TagLanguageIETF elements. Yet the language of tags does not apply to
TagName, but to the content of
TagBinary (after all, one uses a SUMMARY and not a ZUSAMMENFASSUNG for a tag containing a german summary). This means that it makes no sense to set a language for BPS, DURATION, NUMBER_OF_FRAMES, NUMBER_OF_BYTES, _STATISTICS_WRITING_DATE_UTC and _STATISTICS_WRITING_APP (although the release name is commonly an english expression, the version name as a whole is not). While the content of _STATISTICS_TAGS are indeed english words/abbreviations, they are not used as english words, but rather to indicate which other tags contain track statistics tags, so I'd lean to not use a language for it as well.
Given that the default value of
TagLanguage is "und" this means that one can just stop writing these elements altogether.